1. Field of the Invention
The present invention relates to a laser light beam coupling apparatus that couples a plurality of laser beams emitted from a plurality of light sources into a single light beam.
2. Description of the Related Art
In recent years, the technology of coupling a plurality of laser light beams emitted from a plurality of light sources into a single light beam is being developed to obtain a high-power laser light. For example, Japanese Patent Application Laid-open No. 2002-202442 discloses a laser light beam coupling apparatus that includes a plurality of light sources arranged in a matrix shape, a plurality of collimator lenses arranged corresponding to the light sources, a condenser lens, and a multimode optical fiber. Each of the collimator lenses collimates a light beam emitted from its corresponding light source into a substantially parallel light beam and outputs the substantially parallel light beam to the condenser lens. The condenser lens then focuses the substantially parallel light beams on the multimode optical fiber to obtain a single light beam.
Japanese Patent Application Laid-open No. 2005-114977 discloses a laser light beam coupling apparatus that takes into consideration the anisotropy in the emitting angle of the light beam. The laser light beam coupling apparatus includes an array of semiconductor lasers each having an emitting region with identical orientation. The semiconductor lasers having relatively larger emitting regions are arranged in vertical direction, while the semiconductor lasers having relatively smaller emitting regions are arranged in horizontal direction. Moreover, the number of semiconductor lasers having relatively larger emitting regions is less than the semiconductor lasers having relatively smaller emitting regions. An anamorphic element is used to adjust the size of the light beams emitted from the semiconductor lasers. As a result, when the light beams are coupled into a single light beam, the beam spot diameter of the single light beam is reduced in a balanced manner.
Meanwhile, during the process of manufacturing a semiconductor laser, the size of its emitting region in the width direction generally becomes several times larger than that in the thickness direction. The emitting angle of the light beam emitted from the semiconductor laser depends on the size of the emitting region. In the thickness direction of the semiconductor laser (i.e., in the short side direction of the emitting region), the light beam emits from substantially a single point source and diverges by a relatively larger angle. On the other hand, in the width direction of the semiconductor laser (i.e., in the long side direction of the emitting region), the light beam emits from the entire width portion and diverges by a relatively smaller angle. Thus, the emitted light beam has an anisotropic emitting angle with respect to the thickness direction and the width direction of the emitting region. The shape of the beam spot obtained by focusing such an emitted light beam is elliptical. The long axis direction of the elliptical beam spot corresponds to the width direction of the emitting region, while the short axis direction of the elliptical beam spot corresponds to the thickness direction of the emitting region.
Thus, if a plurality of semiconductor lasers, each emitting a light beam at an anisotropic emitting angle, is arranged in a matrix shape, then the coupled beam spot of those light beams happens to possess anisotropy as the beam characteristic. As a result, the beam spot diameter of the single light beam increases in a single direction thereby degrading the coupling efficiency with the multimode optical fiber.
An example of an anamorphic element is a prism, which is high-priced thereby increasing the manufacturing cost of the laser light beam coupling apparatus. Moreover, use of the anamorphic element leads to optical loss such as internal absorption or interface reflection. Thus, it becomes difficult to perform efficient light coupling at low manufacturing cost by using the anamorphic element.